Thermodynamic Degrees Of Freedom Research Articles

Thermo-Magnetostrictive Effect for Driving Antiferromagnetic Two-Dimensional Material Resonators.

Magnetostrictive coupling has recently attracted interest as a sensitive method for studying magnetism in two-dimensional (2D) materials by mechanical means. However, its application in high-frequency magnetic actuators and transducers requires rapid modulation of the magnetic order, which is difficult to achieve with external magnets, especially when dealing with antiferromagnets. Here, we optothermally modulate the magnetization in antiferromagnetic 2D material membranes of metal phosphor trisulfides (MPS3), to induce a large high-frequency magnetostrictive driving force. From the analysis of the temperature-dependent resonance amplitude, we provide evidence that the force is due to a thermo-magnetostrictive effect, which significantly increases near the Neél temperature, due to the strong temperature dependence of the magnetization. By studying its angle dependence, we find the effect is observed to follow anisotropic magnetostriction of the crystal lattice. The results show that the thermo-magnetostrictive effect results in a strongly enhanced thermal expansion force near the critical temperature of magnetostrictive 2D materials, which can enable more efficient actuation of nano-magnetomechanical devices and can also provide a route for studying the high-frequency coupling among magnetic, mechanical, and thermodynamic degrees of freedom down to the 2D limit.

Geometrothermodynamics of van der Waals systems

We explore the properties of the equilibrium space of van der Waals thermodynamic systems. We use an invariant representation of the fundamental equation by using the law of corresponding states, which allows us to perform a general analysis for all possible van der Waals systems. The investigation of the equilibrium space is performed by using the Legendre invariant formalism of geometrothermodynamics, which guarantees the independence of the results from the choice of thermodynamic potential. We find all the curvature singularities of the equilibrium space that correspond to first and second order phase transitions. We compare our results with those obtained by using Hessian metrics for the equilibrium space. We conclude that the formalism of geometrothermodynamics allows us to determine the complete phase transition structure of systems with two thermodynamic degrees of freedom.

Hydrate Modeling Filtration of Salt Liquid-Ice Solutions and Gas Mixtures with Splitting by Physical Processes

The filtration model of the hydrate-equilibrium zone (HEZ) in the mixture of liquid-ice solutions and gas with possible solid-phase salt sedimentary inclusions in a porous medium is studied. Various types of saturating the liquid-ice mixture with gas and salt, as well as salt sediment in HEZ in the absence of a liquid phase are considered. Based on the Gibbs phase rule, various types of dissociative bonds between thermodynamic variables in the problems under consideration are determined for systems with one thermodynamic degree of freedom.

Pressure-aided cooling: Adding thermodynamic degrees of freedom

Pressure-aided cooling: Adding thermodynamic degrees of freedom

Nonlinear dynamics of DNA with topological constraints

The mechanical DNA model is developed to study the nonlinear dynamics, topological constrains of the helicoidal geometry DNA molecule, dissipation effects and influence of the external force. To construct the model of DNA the Peyrard-Bishop-Barbi approach has been applied. We have derived equations of motion for the DNA base pairs in the presence of a damping term and external driving force to follow the Caldirola-Kanai method. The analytical small localized solutions as the discrete breather and the antikink have been obtained by multiple scale expansion method for multicomponent lattices. The impact of the damping effect and external forces on the breather and the antikink propagation has been investigated. The prospects of using the helicoidal model of DNA with the energy dissipation and external force are discussed. The dissipative term and the external force term in the DNA motion equations follow from corresponding Hamiltonian energy representation. The advantage of this approach is the promising way to study both the thermodynamic properties and nonlinear dynamics of DNA system related to the types of the collective modes (breathers, antikinks) as new thermodynamic degrees of freedom. This result allows the formulation of the experimental strategy to analyze the qualitative changes in cell dynamics induced by mentioned collective modes.

Electrons under the dominant action of shock-electric fields

We consider a fast magnetosonic multifluid shock as a representation of the solar-wind termination shock. We assume the action of the transition happens in a three-step process: In the first step, the upstream supersonic solar-wind plasma is subject to a strong electric field that flashes up on a small distance scale $\Delta z\simeq U_1/ \Omega _{\mathrm e}$ (first part of the transition layer), where $\Omega_{\mathrm e}$ is the electron gyro-frequency and $U_1$ is the upstream speed. This electric field both decelerates the supersonic ion flow and accelerates the electrons up to high velocities. In this part of the transition region, the electric forces connected with the deceleration of the ion flow strongly dominate over the Lorentz forces. We, therefore, call this part the demagnetization region. In the second phase, Lorentz forces due to convected magnetic fields compete with the electric field, and the highly anisotropic and energetic electron distribution function is converted into a shell distribution with energetic shell electrons storing about 3/4 of the upstream ion kinetic energy. In the third phase, the plasma particles thermalize due to the relaxation of free energy by plasma instabilities. The first part of the transition region opens up a new thermodynamic degree of freedom never before taken into account for the electrons, since the electrons are usually considered to be enslaved to follow the behavior of the protons in all velocity moments like density, bulk velocity, and temperature. We show that electrons may be the downstream plasma fluid that dominates the downstream plasma pressure.

Infinitesimal Legendre symmetry in the Geometrothermodynamics programme

The work within the Geometrothermodynamics programme rests upon the metric structure for the thermodynamic phase-space. Such structure exhibits discrete Legendre symmetry. In this work, we study the class of metrics which are invariant along the infinitesimal generators of Legendre transformations. We solve the Legendre-Killing equation for a K-contact general metric. We consider the case with two thermodynamic degrees of freedom, i.e., when the dimension of the thermodynamic phase-space is five. For the generic form of contact metrics, the solution of the Legendre-Killing system is unique, with the sole restriction that the only independent metric function – Ω – should be dragged along the orbits of the Legendre generator. We revisit the ideal gas in the light of this class of metrics. Imposing the vanishing of the scalar curvature for this system results in a further differential equation for the metric function Ω which is not compatible with the Legendre invariance constraint. This result does not allow us to use Quevedo's interpretation of the curvature scalar as a measure of thermodynamic interaction for this particular class.

Phase transitions in geometrothermodynamics

Using the formalism of geometrothermodynamics, we investigate the geometric properties of the equilibrium manifold for diverse thermodynamic systems. Starting from Legendre invariant metrics of the phase manifold, we derive thermodynamic metrics for the equilibrium manifold whose curvature becomes singular at those points where phase transitions of first and second order occur. We conclude that the thermodynamic curvature of the equilibrium manifold, as defined in geometrothermodynamics, can be used as a measure of thermodynamic interaction in diverse systems with two and three thermodynamic degrees of freedom.

Physicochemical processes in multiphase systems on metal surfaces containing nano-carbon: Segregation, dissolution, graphene nucleation, and growth

A carbon phase equilibria on the surface of metals during graphene nucleation and initial graphite growth is considered thermodynamically. Three phases are shown to be necessarily taken into account: C atoms dissolved in a metal substrate bulk, C atoms chemisorbed on the surface, and graphene (polycondensed carbon phase). Applicability of the Gibbs phase rule to this particular case is analyzed, with surface tension taken into account as an independent thermodynamic degree of freedom. A specific role of boundary atoms of graphene islands, which can be considered (with some limitations) as an independent quasi-1D phase is revealed.

A General Approach to First Order Phase Transitions and the Anomalous Behavior of Coexisting Phases in the Magnetic Case

AbstractFirst order phase transitions for materials with exotic properties are usually believed to happen at fixed values of the intensive parameters (such as pressure, temperature, etc.) characterizing their properties. It is also considered that the extensive properties of the phases (such as entropy, volume, etc.) have discontinuities at the transition point, but that for each phase the intensive parameters remain constant during the transition. These features are a hallmark for systems described by two thermodynamic degrees of freedom. In this work it is shown that first order phase transitions must be understood in the broader framework of thermodynamic systems described by three or more degrees of freedom. This means that the transitions occur along intervals of the intensive parameters, that the properties of the phases coexisting during the transition may show peculiar behaviors characteristic of each system, and that a generalized Clausius–Clapeyron equation must be obeyed. These features for the magnetic case are confirmed, and it is shown that experimental calorimetric data agree well with the magnetic Clausius–Clapeyron equation for MnAs. An estimate for the point in the temperature‐field plane where the first order magnetic transition turns to a second order one is obtained (the critical parameters) for MnAs and Gd5Ge2Si2 compounds. Anomalous behavior of the volumes of the coexisting phases during the magnetic first order transition is measured, and it is shown that the anomalies for the individual phases are hidden in the behavior of the global properties as the volume.

Quasiparticle degrees of freedom versus the perfect fluid as descriptors of the quark-gluon plasma

The hot nuclear matter created at the Relativistic Heavy Ion Collider has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of quantum chromodynamics quasiparticles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy-ion collisions. The empirical observation of constituent quark ``${n}_{q}$'' scaling of elliptic flow [PHENIX, A. Adare et al., Phys. Rev. Lett. 98, 162301 (2007)] is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. As the hydrodynamic fluid expands, increasing viscous effects may allow for a short time period of ``quasiparticle transport'' prior to hadronization. However, without a detailed understanding of the transitions between these time stages, the ``${n}_{q}$'' scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well-defined quasiparticles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of ``${n}_{q}$'' scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.

A Finite-Time Thermodynamics of Unsteady Fluid Flows

Turbulentfluidhasoftenbeenconceptualizedasatransientthermodynamicphase. Here, a finite-time thermodynamics (FTT) formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The proposed formalism builds upon the Galerkin model framework, which simplifies a continuum 3D fluid motion into a finite-dimensional phase-space dynamics and, subsequently, into a thermodynamics energy problem. The Galerkin model consists of a velocity field expansion in terms of flow configuration dependent modes and of a dynamical system describing the temporal evolution of the mode coefficients. Each mode is treated as one thermodynamic degree of freedom, characterized by an energy level. The dynamical system approaches local thermal equilibrium (LTE) where each mode has the same energy if it is governed only by internal (triadic) mode interactions. However, in the generic case of unsteady flows, the full system approaches only partial LTE with unequal energy levels due to strongly mode-dependent external interactions. The FTT model is

A Hamilton–Jacobi formalism for thermodynamics

We show that classical thermodynamics has a formulation in terms of Hamilton–Jacobi theory, analogous to mechanics. Even though the thermodynamic variables come in conjugate pairs such as pressure/volume or temperature/entropy, the phase space is odd-dimensional. For a system with n thermodynamic degrees of freedom it is 2 n + 1 -dimensional. The equations of state of a substance pick out an n-dimensional submanifold. A family of substances whose equations of state depend on n parameters define a hypersurface of co-dimension one. This can be described by the vanishing of a function which plays the role of a Hamiltonian. The ordinary differential equations (characteristic equations) defined by this function describe a dynamical system on the hypersurface. Its orbits can be used to reconstruct the equations of state. The ‘time’ variable associated to this dynamics is related to, but is not identical to, entropy. After developing this formalism on well-grounded systems such as the van der Waals gases and the Curie–Weiss magnets, we derive a Hamilton–Jacobi equation for black hole thermodynamics in General Relativity. The cosmological constant appears as a constant of integration in this picture.

Near-Critical Gas–Liquid Flow in Porous Media: Monovariant Model, Analytical Solutions and Convective Mass Exchange Effects

We examine a class of hydrocarbon reservoirs whose thermodynamic state remains close to the critical point during the all period of reservoir exploitation. Such a situation is typical for the so-called gas–condensate systems, in which the liquid phase is formed from gas when pressure decreases. Due to proximity to critical point, the mixture contains many components which are neutral with respect to the phase state. This determines a low thermodynamic degree of freedom of the system. As the results, the mathematical flow model allows a significant reduction in the number of conservation equations, whatever the number of chemical components. In the vicinity of a well, the system may be reduced to one transport equation for saturation. This nonlinear model yields exact analytical solutions when the flow is self-similar. In more general case of flow, we develop partially linearized solutions which are shown to be sufficiently exact. The spectrum of examined cases covers the flow in a medium with a sharp heterogeneity and a sharp variation in the flow rate. A significant relative gas flow past liquid gives rise to a convective mass exchange phenomenon which appears highly different from that observed in static. In the case of a medium discontinuity, the convective mass exchange gives rise to a phenomenon of condensate saturation billow formation. A sharp variation in the flow rate leads to a hysteretic behavior of the saturation field.

2D numerical simulation of the interaction of high-power laser pulses with plane targets using the “ATLANT-C” Lagrangian code

The “ATLANT-C” program developed for the two-dimensional (2D) simulation of problems of Lagrangian gas dynamics is described. The difference scheme of gas dynamics with an increased number of thermodynamic degrees of freedom used in the program preserves the plane, cylindrical, and spherical symmetry of the one-dimensional (1D) flows. The approach proposed provides an improved retention of the shape of the computational cell and the solution of problems incomputable with the conventional schemes. The efficiency of the algorithms applied is confirmed by the test calculations and results of simulation of actual physical experiments.

Signal entropy and the thermodynamics of computation

Electronic computers currently have many orders of magnitude more thermodynamic degrees of freedom than information-bearing ones (bits). Because of this, these levels of description are usually considered separately as hardware and software, but as devices approach fundamental physical limits these will become comparable and must be understood together. Using some simple test problems, I explore the connection between the information in a computation and the thermodynamic properties of a system that can implement it, and outline the features of a unified theory of the degrees of freedom in a computer.

Phase Transitions in Minerals: From Equilibrium Properties Towards Kinetic Behaviour Progress Report

Landau theory is derived from a simple atomistic model. The Gibbs free energy can be written in the displacive limit as where Ts = 1/2Θs is the saturation temperature due to quantum fluctuations. The coefficients A, B,… and degeneracies of the order parameter are determined by the conventional symmetry constraints. For T > Θs, G is the classic Landau potential. Solutions for non-displacive systems and coupled order parameters are discussed. – The theory is applied to some model-minerals such as quartz, Na-feldspar, and calcite as typical examples. It is argued that the structural complexity of minerals is often related to several thermodynamic degrees of freedom. The transition leads to coupling phenomena, which are reviewed in some detail. – Non-equilibrium features in crystals which are “nearly” in thermodynamic equilibrium are domain walls. It is shows that domain walls react very sensitively to small changes in the thermodynamic state of the material. New structural configurations are generated in the wall which do not exist in the bulk. – Kinetic processes with continuous order parameters can be analysed using a general rate equation which contains δG/δQ (G is often a Landau potential, Q is the order parameters) as a driving force. This theory draws, thus, a connection between the equilibrium Landau-type theories and kinetic rate theories.

Thermodynamics of Surface Morphology

Classical thermodynamic descriptions of surfaces treat surface orientation as a thermodynamic degree of freedom and thus allow for the possibility of reversible changes in surface morphology as a function of temperature or impurity concentration. The existence of these transitions has been confirmed experimentally. Advances in surface diffraction and imaging techniques now make it possible to characterize such transitions quantitatively in terms of the atomic structure, and particularly in terms of the behavior of steps on surfaces. Statistical mechanical models can be used to analyze the observations to determine the fundamental energetic parameters governing the observed thermodynamic behavior.

Thermodynamic representation of the state of a saturated fluid

The Massieu function of a saturated fluid (composed of one particle species, two phases, and one thermodynamic degree of freedom) is given as a function of the temperature, vapor pressure, surface tension, and chemical potential, the latter being expressed in terms of the bulk densities. It is thus possible to give a complete thermodynamic description of the state of this system that includes the absolute values of the entropy and internal energy.